Some local supply shops probably have classes. General Air in CO has some excellent MIG courses that are well worth the $50-70.
I used a DIY bumper kit on my old Land Cruiser to learn. Just know the limits of your machine. My little 110V one ran out of mustard when it came time for the bigger pieces (think swing out spindle, hitch steel, tow hooks). Some of it I did multi-pass, but most I just borrowed the in laws 220V machine (which I now have one of myself).
Just be a little extra careful when it comes to things like winch trays or recovery hooks as a failed weld there can be costly, but I wouldn't let it deter you. I used the hell out of the bumper I built - wheeling, towing, you name it, and it still held. Vans are a bit heavier duty though.
'06 EB 350, Advanced 4x4, 6.7 Cummins + Allison, 24" bubble top.
'05 Pleasure Way Excel TS V10, still boring and 2wd