Nice to see another ham on the forum.
Like most hams I have Opinions about this topic.
Any 10m antenna small enough to mag-mount is going to be extremely inefficient, and the lack of a good ground plane will really hurt you on HF. Even shortened quad-band antennas are often four to five feet long, and heavy because of all the traps and loading coils.
I'd consider using one antenna for VHF/UHF and a separate one for 10m. Coax loss on 10m is pretty low so you could put the 10m antenna on the back bumper or something like that if you don't want to drill into the van body.
Mag-mounts always seem to damage the finish eventually, so I'm a strong proponent of through-hole NMO roof mounts. I've put them on four different cars at this point, and never had one leak. When I go to sell the vehicle I just put a rain cap on it. No one's ever complained, some buyers saw it as a plus.
That said, there's nothing really *wrong* with a mag-mount on VHF; the performance is acceptable in my experience. I just don't think they're ideal for long-term use.
Consider whether you'll be using 10m while in motion. If not, your antenna options open up a bit, e.g. an 8 foot quarter-wave whip becomes much more practical.
By the way, CB antennas work great on 10m if you shorten them up a bit. Just trim until the SWR is good in the part of the band you like.