PP, I'm reading between the lines a bit, both by scrutinizing your intro post and looking at your profile and making the assumption that you're interested in selling something New Haven/Coal/Neo-New York-ish on a mobile basis. If that's the case, believe it or not, that's relatively uncharted territory here.
We have members with grills, both using wood or gas, making Neapolitan pies, and we have a member with a van fitted with a full sized gas deck oven producing something Coal-ish,http://caseyspizzas.com/
but I can't seem to recall any member doing anything along the lines of modified grill coal style mobile or wood fired coal style mobile.
If you have the money, I don't think you can top Casey's setup for that kind of style. That's pretty ambitious, though, and I get the feeling that you're looking for something smaller scale.
Casey got his start with a little black egg (LBE) and, while most of the members using LBEs commercially have striven for Neapolitan, New Haven, with it's longer bake time, is a bit easier. It sounds like you want to be somewhere between an LBE and a truck fitted with a Marsal, but, honestly, I haven't seen any middle ground.
I guess, in theory, nothing's stopping you from buying or making an oversized gas grill and putting it on a trailer. Stainless steel would stand up nicely to the weather, while still not breaking the bank like a Marsal would. A grill would be exponentially lighter than a WFO, so you wouldn't have to go crazy about reinforcing the trailer for the extra weight. I would suggest seeking out an extraordinarily high BTU grill for this purpose, though.
Before you go full scale, I would definitely make sure you're existing 'small scale' grill pies are perfect so that you know what kind of modifications will be necessary for the large grill. Out of the box, there's no gas grill that can, with a stone, put out Pepe quality pies. I normally encourage home bakers to strive for better than commercial pizzeria results, but, since I had the chance to try Pepe's a couple months back, I think they are more than a worthy enough model to emulate. A typical gas grill, to produce Pepe quality bake times, will require some modifications, such as a lower roof, a less conductive stone and/or some kind of deflection under the stone. A gas grill, with the lower BTUs involved, has a lot less room for error than an LBE, but if you can dial in the all the elements, you should be able to see something Pepe-ish- if you haven't already.
What kind of BTUs are you working with now? What's the shortest bake time you've been able to achieve?