My first ? is: Does your van fit in your garage? <g>
I am presuming your antenna are for 2 meters??? How about a magnet mount on roof of van I use this method. Do you have a mini van or full size van?
For HF operation I have used a mount bolted to real bumper and I have used a trailer hitch mount. sometimes taking the ball out and purchasing a mount that will fit the hole or using the safety chain hole and get a "BAR" mount and affixing it in the hole with bolt and nut. Then I have a 3 foot mast and then put the antenna in top of mast to get antenna above the van.