My experience has been that an automotive scissor or bottle jack is often not hefty enough for a boat or travel trailer. With a vehicle you're typically just lifting one corner. With a trailer you're lifting the whole side of the unit, ie. much more weight.
I carry one of these in my Yukon since I often tow a 28' travel trailer as well.
You just wedge it under the axle, pull forward a bit, and the jack rotates under the axle and lifts it up. I place a chunk of old carpet between the jack and the axle so it doesn't scratch the axle.
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, Acme 1285, PPass
(previous) 2001 X5, 1991 TriStar 190