I'm with JD....it happens...period. Try to plan ahead for your clean-up in the pits. For example, a shop vac is really useful before you dive inside the car or engine bay to start working. If you are still in the building stage, try to plan for easiest possible disassembly. That is what gives you the edge, when it's time to start fixing everything that is corroding. Think twice about hidden bolts or fasteners with difficult access. You'll have to fix everything; try to make it easy on yourself.
Oh yeah...almost forgot... NO floor mounted electrical. After a hard lesson in '97, I kept everything that counted (on the 797 roadster electronics) in a bracket mounted Tupperware box. I passed the wiring through a right angle cut in the bottom, then glued the cut shut. I kept the lid tight with nylon straps and buckles from the sporting goods store (dont use bungee cords, or it'll squeeze open gaps). The computer, relays, etc. are still in good shape after quite a few passes over the years.
A trick I used on my ocean racers (sail) was to mount a Tupperware lid (with a hole cut in it) to a bulkhead (on washers to keep it flat). I used the box as the removeable lid. This was for the back side of gauges and intruments that had to pass through a panel. This method leaves easy service to wiring, knobs, adjustment screws, etc. while keeping the back side of the instruments dry and corrosion free. Leave enough wire coiled inside so you can pull the "box" off to get at the item, without breaking the sealer around the wire pass through.
Regards, JimL