had a long deal typed and lost it, crap. here goes agian.

We have a late 90's GMC with the vapor system and a dump bed,  seems to be a good truck.  Also have a 04 GMC with the liquid inject on a 8.1 with auto, 12' van box and pull a car trailer with a 10,000 lb 277 cat skid steer on it.  goes good at about 5 to 7 mpg.  Have to let the pump pump up on pressure on the injection or it will not run right,  turn key and wait like 30 seconds to start. 

Have alot of older trucks and pickups on propane aswell, the injection systems might be some $ when they go bad we will see.

Like Farmboy99 said there is a guy in town here that fixes them up, that is the only reason we have a couple.  Local dirt guy has a bunch on flatbeds and service trucks aswell.  http://www.wittrockenterprise.com/

As for taxes your on your own.  Here we have to have plates on our sprayers and floaters but can run off road fuel.  Farmers don't have to have plates on there self propelled rigs,  I think but I have never seen them with plates.  If you don't slide the sprayer out and use it as a flatbed you should be able to use "off road propane" out of your dryer or shop tank.  at least here!