Hi I have been thinking of starting a coffee van and the obvious choice would be a gas powered machine but what doesn't seem to exist is a dual boiler gas powered machine. What I was thinking is if I bought a dual boiler machine such as a la marzocco Linea could I convert it to gas?
I have seen that Astoria make a gas kit that includes everything needed to convert their machines. If I bought 2 of these kits I don't think it would be too difficult to modify them to go on each boiler. Anyone have any input or advice on this?

If you haven't yet, you'll want to read and look at the pictures from:
Gas/propane kit for Astoria arrived - Now what?

Then hash out your plan for installing 2 of them in a 2 boiler machine. If you want to share your plan, people will probably share their advice and opinions.

The better bet for a coffee van is going to be a commercial spring lever machine. Think about how you will be powering the equipment. Gas is your best option no doubt. But with a pump machine you need electric too. Spring levers come in configurations that have little to no electrical parts. All you will need is to power the pump for boiler filling. This can be just a rechargeable 12 volt battery.

Of course you will need a generator for grinders and other equipment but adding the machine on that feed will require a much bigger generator. There is a very fine balance on powering all the equipment.

Going gas for all boilers and cooking equipment, etc will keep your costs considerably lower for powering heat making devices.

This old OE video may be of interest.

I don't think you will be able to use the Astoria gas valve on a brew boiler. It is designed for 1.5 bar steam input, 9 bar hot water is unlikely to work. Switching the brew boiler to digital temperature control would work, but you will need to source a proportional gas valve with the appropriate flow characteristics. It might also be necessary to relocate some of the internal electronic components, even when shielded there will probably be heat rising in new places in comparison to an internal electric heating element.

My vote would be for a multigroup lever if you want to go with gas heating, although I seem to remember seeing a few CMA/Astoria HX machines with the gas kit installed. Their lack of popularity may be all that needs to be said.

With modern high capacity storage batteries and DC/AC inverters, I don't see why you couldn't just power your machine(s) electrically. As someone else pointed out, you'll also need to run your grinder and probably a refrigerator. Unless you're planning to set up in a 3rd world country ( and I don't think France has been demoted to that status yet), bottled gas is not the best way to go.