I think you would be better off with a Sport (SWB) if you can find one. Probably one of the older versions (known as the A-Series). Bit older than you were thinking but here's why.
I have marshaled myself in the past, everything from the welsh forests and service on the RallyGB to clubman single venue events. The Sport (as I found on the recent Snowdon FOG meet) will happily carry all the luggage I needed for the weekend with the rear seats up. these can be dropped down should more space be required.
The SWB might be more bouncy off-road, but I would think the shorter lenght and turning space (not actual turning circle, think more about negotiating tight turns and parking up off the stage) would be of benefit.
The reason I am thinking of one of the older models is the higher ground clearance, although on the Snowdon meet, two later models (the age you were looking at) were present, on road tires, and easily coped with every lane. This was far more than you would ever face on a stage, even in the forests. Also the older dash is more friendly to having things placed on it which could come in handy. The reason I am thinking of an SWB is that you already have a big 4x4 in the Disco. If you need lots of space take that, least the SWB gives you as opposite an option as you can have in a 4x4.
I'm sure others will chime in with thier thoughts, we do have some who use their Fronties for running Radio posts on rallies so can give you a very informed opinion.
Steve Coleman95 Vauxhall Frontera Sport, 2.8TDi, Caribic Blue.

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