Guitars and violins are obviously very different instruments, but there are a lot similarities in how they are cured. The same with ukuleles, banjos, mandolins, and anything else with strings and a wooden body. Some will use 4 foot lamps, some with use 6 foot lamps. Generally speaking, the ends of the lamps are the weakest, so you should figure 4 foot lamps for 3' items, and 6 foot for anything bigger than that. This allows enough length that the top and bottom of the instrument will get exposed with a minimum of effort. You will still to add reflectors in the top and bottom of the box, but it is pretty easy and cheap: A roll of Reynolds kitchen aluminum and a $7 can of 3M spray glue.
What makes a proper rig tricky is the fact that you really, really need to expose all 4 sides at the same time. A medium sized rig for electric or acoustics will use 16 lamps, 6 foot long, powered by four SunHorse ballasts. These lamps are very long lived, however, so while the upfront cost will be over $1000, the lamps are designed to last 1000-2000 hours (depends on number of cycles), which is 60,000 to 120,000 minutes, and the average cure takes just minutes. Worse case scenario, the rig costs you less than 25 cents per use (and that includes the cost of hardware, so it gets cheaper over time). Electricity per use will likely be less than a quarter as well. Obviously, it very cost effective to use this kit.
The above image shows the most common configuration for professional guitar builders. The lamps are done in a 5/3/5/3 configuration. Hobbyists can get by with a 12 lamp configuration, using a 4/2/4/2 configuration. The trick part is the wiring at the hinge, which needs to be cut into, then use stranded wire over the hinge itself, so it won't break after repeated use. Hobbyists can probably skip that step. It is perhaps possible for a hobbyist to do a 3/1/3/1 for electric guitars only, but that is untested and will likely be much slower to cure, in order for all areas to get enough UV. Now you just need to hang the guitar from a cross member of the box you built, and you are ready to cure some resin.
Painting the box white inside (or any other color) is useless for reflecting UV, so don't bother. You might add a coat of UV finish, just to keep the unit from dripping sawdust onto your final product, then turn it on for an hour to make sure it is super cured.
People looking for the fastest and best cure will go ahead and use aluminum foil (and the spray glue) on all surfaces inside the cab, with the shiniest side facing the center of the cab. It isn't required, but honestly, it is pretty cost effective since you are exposing all four sides of the guitar at the same time. Even a few percent adds up over time.