My wife keeps telling me that sugar isn't the only thing that melts so I probably should be concerned.Don't drive in the rain if you think you will melt!
You may have a problem if you drive Out of the Shop in the pouring Rain BUT, I would bet if you drive an open car you are going to be WET going back to the Shop at some time........You will not melt and things will dry out........Have Fun.....
The faces of gauges are pretty well sealed , the back of the gauge where , if immersed, could do damage is behind/under the dash , don't see that as a problem. Most autoomotive upholstery is synthetic & dries very quickley , I'd guess mine gets more water when I scrub them than in rain..For my build the achilles heel when it comes to any form of wet would be the gauges. Electronics and wet do not play well together. The interior will be done in bed liner paint, so no worries there. The yet to be decided on seating is a worry...especially with automotive seating.
During construction I'll be relying on a car cover. Eventually the plan is to have a tonneau cover made for mine. Rain when on the go will be dealt with by getting parked as soon as possible, and getting the tonneau on. Unless there is shelter near by, I'll just get wet.
Front heck ! The rears throw it in worse...Rooster tails from the front wheels. BRILLIANT