That Bridger Boiler is spendy!
I built a 120V system for about $50 consisting of hot water heater element, extension cord, cattle feed bucket and some silicone sealant, coupled with an electronic controller that allows me to keep the water at a specific temp. Works great and doubles as a "sous vide" cooker at home. Would not work if you don't have AC power, however.
The car wash thing may or may not work, but the one where I hunt in Montana has big signs stating not to do so.
Regardless of what you end up with, there are a few things that I suggest:
1. Get all of the hide, lips, tissue, eyeballs, lower jaw, etc. out before the first dunk (I use a coat hanger to pull out brains),
2. Protect the antler bases - you can easily decolor them during the process,
3. I always add some Dawn dishwashing liquid AND sal-soda (Borax) to the water - combined, they do wonders to break down the oils/fats,
4. Simmer, don't boil, as boiling can weaken the bone. I think the best euro mounts keep the nasal cavity bone intact but these water methods generally destroy them - beetles do the best job with that,
5. Remove occassionally and pull off bits and pieces. Teeth may fall out. The whole point of CWD regulations is to avoid potential spreading, so do the right thing when disposing of the liquids and bits.
6. If you're going to spend the time to do it, do it right the first time and get it as clean as possible,
7. Once you get home, do NOT use bleach - it will weaken the bone and yellow over time. Use Baquacil Oxydizer, which is a strong pool chemical that will make the bone white as can be.
Good luck!