There is rarely a need to crawl directly underneath a TT. Most maintenance involves work at the axle ends and that can be accomplished by jacking the axle and using a jack stand as a fail-safe.
I don't care for those ramps since if it rolls up easy (never did for me), it can roll down easy. Also, once you have the trailer raised and sitting on ramps, you can't work on the axles/hubs.
If you plan on doing extended work underneath, it is better to use cribbing at multiple locations so that sudden drops are eliminated.
