Cheap and Easy Spray Booth:

 This is a pretty straightforwards tutorial on building (like the name says) a "cheap and easy" spray booth suitable for priming, sealing, and basecoating with aerosol sprays. I am simply providing step-by-step instructions, and am not to be held responsible for anything that may happen through the use of a spray booth such as this indoors, i.e. toxic exposure to paint fumes, exploding furnaces, or a light dusting of primer on someone's antique furniture. Also many thanks to Alf from the Relic News Forums for the original instructions!

With that out of the way, here's the materials:

• 1 reasonably sized, durable cardboard box
• 1 roll of standard duct tape
• A supply of micro-fiber filter as can be found at most home improvement-type stores
• A heavy-duty commercial-grade vacuum, AKA "Shop Vac", etc.
• A medium-sized plastic bag

Here's a picture of the assembled (and frequently used) spray booth I set up myself:

 I would suggest that you set it up in a well-lighted, well-ventilated area such as a garage. I would also suggest that you raise the level of the booth bottom to a comfortable height to allow for easier spraying when the time comes - mine's at relatively floor level due to space considerations, but a small stool underneath gives me enough clearance to easily see all areas of my figures when spraying whilst sitting on the floor.

 To start, cut a piece of micro-fiber filter (seen through the hole in the back of the box) a little larger than you actually want the opening at the back of the box to be - try to make the hole reasonably large, as the whole point of this setup is to remove excess paint vapors from the air. The next step is to cut a hole about 1" or so smaller than the piece of filter in the back of the box, relatively centered behind where you expect to do the majority of your spraying. Leave a reasonable border of cardboard for the filter to sit flush against on the back of the box.

For reference sake, this is what micro-fiber filter looks like in its natural state:

 Next, tape all the seams of the box so as to prevent excess paint being sprayed from escaping out any holes or crevices - ideally, you want as much paint as possible to be drawn towards the filter when using the spray booth. Taking your plastic bag, cut a hole in the opposite end of the opening, or, alternatively, cut the length of the bag down to a more manageable length. The purpose of the bag is to act as a funnel between the hole at the back of the box and the nozzle of your commercial-grade vacuum.

 The tricky part now is to tape the sides of the filter down to the back of your booth over the cut opening so that there are no gaps and the filter sits flush and overlaps the hole on all sides - with mine, I used overly long strips of duct tape on all four sides and made sure they overlapped at the four corners around the filter. The filter doesn't necessarily need to sit into the opening, but the edges do need to be airtight against the box for the next step.

 For the final step with the box, tape one opening (likely the largest) of the bag over both the hole and the filter from the back of the box. As can hopefully be seen from the picture, I made a similar overlapping square of tape around the mouth of the bag against the box and also taped from the bottom of the box over the top of the sealed bag edges and onto the top of the box - this is to prevent the tape and bag from peeling away from your booth from the weight of the vacuum hose, which could be very messy if it happened in mid-spray session. (Note the strategically chosen Games Workshop bag used as a funnel: reduce, reuse, recycle, I say!)

 Prior to initially spraying, you will want to taper the bag via wrapped duct tape so it fits snugly and tightly around the nozzle of the vacuum. With my box, I made a "collar" of sorts to fit around the nozzle of the vacuum, which I then secured to the nozzle itself with an additional piece of tape - although this is actually an extra vacuum I have, it's occasionally useful to be able to separate the vacuum from the attached spray booth if I need to use it for anything else. Likewise, my spray booth is set up on the floor and fairly low, so I have a length of wood to prop the hose up so the mouth of the nozzle sits at roughly a right angle to the back of the filter inside the bag - it gets better suction this way. If you sit the entire setup on a shelf or something, this prop might not be necessary.

 Hopefully this is all pretty self-explanatory, but let me add a few parting thoughts. The vacuum is used whilst spraying to draw excess paint and fumes towards the filter and interior of the box - ideally away from yourself and the area around where you spray. To do this effectively, you need a pretty strong vacuum (mine is 3.5 horsepower) - the stronger the suction, the less airborne paint and fumes end up in places you don't want it: your lungs, your parked car, or nearby sources of flame. The micro-fiber filter is there to prevent the airborne paint particles from clogging up your vacuum itself - and you will ruin a perfectly good vacuum if you skip using ultra-fine filter material or if you fail to change the piece of filter out when it starts to become clogged with repeated spraying. For the sake of brain cells and your overall health, only spray in open, well-ventilated areas and not anywhere near open sources of flame: paint fumes can easily build to toxic levels in enclosed spaces; can kill off massive amounts of brain cells as chemicals are absorbed fairly readily into the bloodstream via the lungs; and can cause an explosion if allowed to build up anywhere near a source of flame or heat - this includes the pilot lights of furnaces and water heaters, cigarettes, and space heaters.