I talked to Nathan at XSPower today, and they are currently in development on their Lithium line for automotive applications that use an alternator output to recharge. At this time their lithium line is only for total discharge service, focused on racing applicagtions like ProStock where you need to start the vehicle, provide power to run for a few minutes, but recharge via a wall plug DC charger, specifically designed for their batteries. This is their LR48 unit, which is computer controlled output and dedicated wall charger in the $2000 ballpark. They have not yet determined the specifics of packaging but expect size to be something like their 680 or 925 units in their AGM (absorbed glass mat) batteries. Their AGM line is similar to that from Odyssey, but XS may have a bit more power - hard to say as they do not print their specs the same way.
Nathan estimated that their lithium street automotive line is at least six months out at this time. All lithium units will have internal computerized technology, so an automotive alternator friendly unit is going to be several (many?) times the nominal $120 price for an AGM unit. Looks like a sealed AGM style is my ticket.
Ken, as noted above if you can point me to pictures of your under dash installation I would love to see your approach.