I got my Leonard alum top off of Craigslist for $50.00. I use my truck with the cap on some hunting/camping in the fall and early winter and my off road use is mainly graded forest roads - light 4x4 use at best. My camping set up is just a "roll-a-cot" brand cot (fits great with no middle leg tight up against the side of truck; most cots have a middle leg in the way) ,and some plastic storage bins, water jug, stove, portable table, folding chair, etc. Maybe 10+ nights a year in the truck and for this reason have not done a platform build or other neat fixes I have read about here. I do run a fan and a light.
I would offer that the advantage of the Alum cap is weight. I can lift it off myself, which I do several times a year when I need to carry bulk mulch/gravel, etc. Downside is it is noisy in any rain and without the fan running, condensation is a problem...I need to insulate the inside ceiling, but do not want the extra weight of carpet, might use 1/4" closed cell foam like sleeping pads and spray adhesive - perhaps this fall.
If I was leaving the cap on the truck all the time, I suggest a fiberglass cap is the way to go.
Last thing is that due to my normal "light" off road operation, I can just wedge things in and I am good to go...but once I did go a little wilder and found out that anything really "off road" requires some good compartmentalizaton and secure restraint to avoid damage/mess...if it sounds bad "back there", it is.
Frank
95 Chevy 4x4 1500-SB
Leonard Cap