Have used Herculiner and Rhino on a couple of small fiberglass trailers that get light duty and they are not holding up very well. I classify both of these products in the same durability as paint and to be used for cosmetic purposes only.
For actual protection, including heavy abrasion, go with Line-X. Just had my 3rd truck bed done yesterday. A 2002 Longbed that had had a heavy rubber mat, coolers and fuel tanks banging around in it. I drove over and waited for them to do the work.
The bed was filthy (I had removed the 5th wheel mount rails but not cleaned anything), had a number of extra holes from previously mounted tank accessories and such and some deep dents in the wheel wells. They banged out the dents, closed the holes, cleaned everything, prepped and masked and sprayed. 2 1/2 hours later I drove away with a new looking bed.
Total cost for over the top coverage, including 6 stake pocket retractable tiedowns was a few dollars more that $600 with a lifetime warrantee. I consider it cheaper than all the others in the long run and definitely worth it when it comes to the amount of time I would have spent and the sore muscles I would have had from the sanding and bending.
(and, no, I don't have any connection, whatsoever, with line-x. Don't even have anyone I know that works for them. )