Four good chocks. I also have a set of wheel locks (police style tire boot) for security but they also will prevent the wheel from rolling.

Wheels chocks will work fine. I do it all the time with one or two on an incline like yours. (usally two) Electric brakes would work fine untill the battery gives out. Surge brakes might leak down. I would trust wheel chocks over trailer brakes any time. If you sleep better with a chock under each tire that is the way to go. One will hold it. Two is safe, Six is silly but better.

Ok - thanks for the feedback. Chocks it will be I had an medium set and just found a large set. I will do all 4 tires just to be safe. I asume I should let the trailer roll forward and get some presure on the chock before I un hook right ?

We had to swap trucks on a hill once. The tranny blew on the way up to Lake Winni in NH. It was a LONG azz hill so backing down was not an option as we were almost to the top. We put every bolder behind the tires that we could and prayed :D:D

Just run a chain thru 2 wheels as a backup to the chocks.

DAMN GOOD IDEA.

Some smarta$$ kid might kick your chocks out just to watch your boat crash thru the house across the street.