2004 GMC ? I would not use the stock OEM receiver with any extension , they were weak. I replaced mine with a
CURT 2.5"2.5" ext. barYou will add a bar that fits 2.5" into the recvr. and the other end accepts any standard 2x2 head . The bar sold is 48" , you cut it down to whatever length you need to clear the camper bumper .
.....You will need to add a length of safety chain and a longer trailer connector plug .....
If you remove the trailer and camper you will want to remove the ext. bar otherwise someone will bang into it .