I know this is an old thread, but I have the same question as OP, and this thread answered some of my questions (thanks, Joshua!).
After looking at Parkit360, Trailer Valet, and the Camper Trolley, I've decided they all have significant weaknesses: 1) they're an extra thing to lug around, attach, and detach; and 2) they can't pull a trailer uphill, they must push it d/t lack of downward force, limiting your placement options. So the Purple Line movers seem to be the way to go assuming I can get an appropriate tough but soft jack wheel. I have an inquiry out to Purple Line regarding the adequacy of their own heavy duty dual wheel caster.
One problem with Joshua's setup ishis 1000-1200 lb tongue weight; that's pretty extreme, possibly due to his application of food truck. Mine is a 19' Bambi, about 350-400 lbs tongue weight (I've moved my batteries to just in front of the axle).