Hotbach...
Are you extending a home studio into a van? Or are you using the same equipment from your studio, and when someone calls up and needs remote recording, you just load the van up with your studio gear? Or do you actually have a full on Digital Diesel that is perminantly outfited with gear?
I am sorry, I do not have any experience with this kind of thing. As far as marketing is concerned, a good website with MP3s, gear list, and remote studio features/capabilities is a good start. And for Pete's sake, if you are no Rembrant with HTML and JavaScript, get someone who is to do the site for you.
Then I would literally print up business cars with your website on there and your contact details... print up flyers (proper ones, not shit Xerox copies) and ask music stores if you can display them there around town and in neighboring towns. I would also call churches (the more Baptist and gospel the better) and explain to them your service and that you would appreciate a thought around time for them to do their Christmas choirs etc...
I am also a HUGE advocate of after you have a few projects under your belt you ask those envloved if they would mind having their work displayed on a promotional CD of your studio. Then you take the CD and have it properly reproduced by a commercial reproduction house... and give those things away for free like water to any potential clients.
All of this may seem excessive in the $$$ department... but think about it like this. For the price of a descent 24 track digital HD recorder or a good Mac, you could have Business cards, a descent functional website, flyers, and 1,000 promo CDs to give away. And if those marketing tools yield even 2 or 3 won business oppertunities, then they have paid for themselves, and if you are worth a damn at Audio engineering, they might open the door to long term repeat clients.
This is my $0.000002 cents worth. I am sure that you thought of all this already. But maybe I offered something up for ya.
Well let me ask you a question while I have you on the phone... When you said that you have finally gotten all the gear you need for your remote van set up... what exactly are we talking about here? Could you give me a quick gear list run down.
Mixer: brand/# of channels/analog or digital etc...
Recorders: Digital or analog? HD unit like the Mackie HDR2496? Or a PC/Mac?
Monitors:
What are we talking about here as far as gear goes?
Good luck man!
Mike