Hans, doesn't matter whether you park it level. The roof itself will likely not leak. The leaks will come in the holes: lights, horn, a/c, antennas, windows. The windows seldom leak *if* the drain channels allow the water to get out, that's what the little slots are for (which are supposed to have plastic covers to keep the bugs out.) Replace the Schlegel channel for the front windows so they slide easily, be sure to get it from someone with fresh stock. No glue in the channels for that! Get *all* the old caulk out before you use new. Polyurethane (both the stiff kind and the 'self-leveling') will be your friend. Eternabond as a last resort.