I'm not certain about the icom 2820..I've never HEARD of one having an 11 meter conversion done on it, but I know the yaesu 857d is a very good sounding rig on the 11 meter band, even on AM (not just SSB).
Fiberglass roof makes roof mounting antennas a moot point, no antenna worth noting would get out well when mounted to fiberglass like that. Best option is going to be GOOD ball mounts (an old Antenna Specialists ball mount, NOT a radio shack piece of trash) bolted to the side (need access to the space between the outer sheetmetal and the inner sheetmetal for this), second best would be a couple of good heavy mirror mount brackets, screwed into the side metal with ATLEAST 4 #14 stainless sheetmetal screws, but bolting it with four 1/4" bolts would be better if you can get to that same space as described for the ball mount. You can get the mirror mount brackets at radio shack, but buy a higher quality stud mount for the antenna, such as a predator 10k hex mount. You can buy predator 10k hex mounts at www.predator10k.net.
As far as the antenna goes, a wilson 5000 trucker would do well, just make sure to use a long enough bottom shaft to get the coil above the roofline..it doesn't have to be far, just so long as the entire coil is above the top of the roof.
For the scanner, I think a through-glass antenna works OK for them..just stay away from the through-glass antennas for the CB and ham rigs.
If you operate in the 2 meter band (or any band outside 10 meters really) you're going to need atleast one more antenna..I've only used home brew antennas for 2 meter, so I can't offer much advice as to brand, but figure on a fender lip mount, or another mirror mount on the OTHER side..If you can post some pics of each side of your van, I'll see if I can come up with some ideas for specific spots for mounts.
Damn, If i saw a van like that with 4 antennas on it outside my house, i think i would quickly format all my hard drives just in case of a police raid! Not that i have anything to hide, i do.
Um, I guess this is where you put something witty.WITTY
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Nice looking van, I'd go with a mirror mount bracket on the drivers side right behind the drivers door, as high up as you can get it on the metal. Go with a wilson 5000 trucker, use a long enough shaft to get the whole coil above the roofline, and drill a hole to bring your coax in through. Use RG8x. Second choice would be a hood/fender lip mount on the drivers side..either with an angle cut to keep it perfectly vertical, or use a flat mount infront of the hood screwed to the top of the core support. Bring the coax in through the firewall/doghouse. You could mount on the passenger side behind the rear side door, but thats not an optimal location for use on the highway..Whatever you do, ground all your doors to the body, and your "hood" to the body..the braid from some old coax works great..Also, ground the exhaust to the unibody with some braid strap at each end of the vehicle. Subtle mods like these can help make up a LITTLE bit of the performance loss for going with a form over function antenna system..I'm going to attempt to attatch a couple of the pics I tagged with potential mounting locations. The yellow circles mark potential mounting locations.
A good place to look at some mounts is http://www.premiere-electronics.net/
There are several that would work well on your van..Stainless is best, aluminum works pretty well too though..Firestik SS-204A or Firestik SS-274a mounts from that website might be good choices..Firestik SS-64AGM GM Sport Mirror Bracket MIGHT be a good choice too, but pay attention to what size antenna you put on it.. Try to spring for the "monster stud"..thats a good strong stud for mounting vertually any antenna you want.
Stay away from the fiberglass antennas ESPECIALLY the ones under 4 ft long, anything under that is going to be a very poor performer. If you REALLY want to use a fiberglass antenna, get a francis..they're the best of the fiberglass antennas..you'll need an external SWR meter to tune your setup no matter what you get. The wilson 2000 trucker is also a good choice for an antenna for 10/11 meter use..
Hope all that makes enough sense to be of some help.
The ham depends on what band you're gonna be operating on..Those mounts are mainly for the CB(11 meter) and 10 meter ham antenna choices..Premiere has a couple of mobile scanner antennas that are roof mounted, they should work on a fiberglass roof and are fairly inconspicuous..