Re: Rivit spacing
What do you have currently as spacing between rivets and what gauge sheet metal is being used? Are your skins smaller sections or larger sections (covering one or more windows per section)?
Personally I do not think you will have much of a problem with overdoing the rivets. As long as they are not buttoned right up next to one another (or spaced far to apart) you should be fine. Even on my bus there are seams where the rivets are spaced at roughly ~1" apart and at times spaced upwards of 2-3" or more. It all depends really on the gauge of the skins themselves, what stresses they will be expecting to take on those parts of the bus and how/where they are mounted structurally to the bus itself. To many rivets in metal is a kin to putting to many nails in a 2x4, rendering the structural strength of the material to be weaker. Too many is overkill as you stated... just as not enough will lack in structural strength.
Edit: You may notice that where the seams and edges overlap/end that there are more rivets as opposed to the number of rivets in places they attach off of the edges (centrally located within a sheet for example). I am not a professional metal worker, and I assume you have the understanding of what I said earlier in my reply. Perhaps others will chime in as I do not see a consensus as I look into other threads of those who have done the same kind of thing. It seems to be one of those tidbits people leave out.
