Silicone or?

I believe the black RTV is for motors (or anywhere) where higher temperatures are anticipated. Either will work; you could pick a regular silicone that's black for aesthetics.

Thanks!

For the body to pan, pretty much any silicone caulk will work. Don't bother with the specialty automotive stuff (Permatex, etc), just grab some regular 10 oz tubes of 100% silicone caulk (DAP brand or other) from Lowes/Home Depot/Ace/etc in black or clear.

I used stainless steel bolts on mine - hate stuff rusting. They were just a few $ more than carbon steel.

Thanks again.

Yeah I like to use stainless too. Well worth the extra coin. Also have a bolt place near work (boltdepot.com) that has nice hardware that cleans up things.  

When using stainless steel fasteners, use never-sieze on the threads or the "GALL" monster may raise it's ugly head.....

Just looking for knowledge here. You fellas seem to take the caulking of that joint pretty loosely. What is the purpose of the caulking here ? Adhesion, sound deadening, waterproofing or what ?

Waterproofing. You'll have gaps there if you don't have some sort of gasket or sealer. VW used rubber or adhesive foam. Probably stops some squeaking too. On the VW pans I've seen, there are dimples around every bolt hole specifically to maintain a gap between the pan and body so you don't completely crush the gasket. You can't get full metal to metal contact around the pans.

Just be aware that stainless steel bolts are only slightly stronger than a Grade 2 steel bolt. If you need both good strong bolts and bling, use chromed steel bolts (Grade 5 or 8 or metric equivalent) instead.

Grade 2 steel bolt 1/4"  minimum tensile strength 74,000 psi

18-8 SS 1/4" bolt minimum tensile strength 100,000 psi

Grade 8 1/4" bolt minimum tensile strength 150,000 psi

Here's some additional clarification on a 1/4" bolt (Fastenal reference):

          Tensile (psi)       Yield (psi)

Grade 2      74000            57000

Stainless    100000 (+35%)   65000 (+14%)

Grade 5      120000 (+62%)   92000 (+61%)

Grade 8      150000 (+102%)  130000 (+128%) 

Stainless's low yield strength means it's going to permanently stretch/bend/deform not much better than what Grade 2 gives you. And unless you are special ordering stainless bolts, you aren't going to find any of the stronger alloys.

Getting back to the caulking, don't be afraid to use a lot.  I used five or six standard (1-1/2") tubes of clear silicon caulk in a caulking gun on both of my builds,  put it on thick enough to squash out and make a total seal, ESPECIALLY all along the rear of the cockpit.  It's easy to clean off the excess and you won't be sorry for using a lot later on.

I believe you must be using a pan and cauling the body to it.  While you are at it, look for the

square spaces where water would slosh forward of the rear wheels and drain down into two spaces maybe 4" x4" and 6 " deep. These spaces should be fiolled with silicome and mine took 3 regular size tubes on each side.  Otherwise you are going to be able to surf in your Speedster if to drive through a heavy downpour.  John Steels gets credit for this important fix---it worked for me and I have a totally dry floor in even strong downpours.

Thanks again all for the advice. Good stuff.

And yes the stainless is nice until it galls. What a bitch that becomes. You learn not to force pretty quickly.