He tried sealing the external lower trim where the side meets the bottom but it is still leaking. Any ideas where he should check for the leak? Windows? We do have Vista Vues. They don't appear to be leaking. Is itCheck carefully at the base of the door frame. Water can run down door frame and find an opening at the bottom into floor area if everying is not sealed tight. Rub rail chalking may have to be extended. Look for gaps where rail meets body and seal gaps. You might want to remove some of that low rub rail you have already chalked and see condition of body under it. Involves taking out vinyl stripand drilling out rivets. Not a complicated job if you still suspect that area. I would recaulk your vista vu windows, the odds are this or the window above is the culprit. I am sure you have been judicously applying water at select points to see if you can isolate the problem.
I had experience on my vintage '56 bubble where the banana skin was rotted thru right at the floor level and water was just running straight into the floor. Solved problem by replacing the banana skin. Had leaks a bottom of door frame also and chalking took care of that. Rub rails have leaked on both the '56 and my '78. Chalking seems to have solved the problems.