Hi FT RV
I have an Aspect 30J... 2015 model and I love it. The fiberglass roof is tucked into the gutter channel, (I guess that's what it's called). It is sealed and you do need to check it at least annually. It is sealed with a sealant that will crack, more often at the very front edge. I have found that by pressing on the edge of the roof where it is tucked into the gutter you will see if the sealant is viable without cracking.
My Aspect has approximately 12,000 miles and I have traveled in the NC mountains and it does scream when climbing as my unit has only a 5 speed transmission. But it does pull up hill well while towing a 3500 lb. GMC Terrain. Down hill, using the tow-haul mode is a real winner and hasn't required a lot of braking. I do use the tow-haul mode both climbing and downhill.
Good luck in your search !