question

This would probably work.
The PV Voltage varies each time the controller performs a MPP scan. Even in constant sunshie, you'll notice the RPM of the fan change which you may find annoying if you're in earshot.

Thanks - I will look fo a quiet fan, it won't be a problem after dark! Oh...but maybe in the morning in the summer.

Forgetting the 140W record for a second, what's a more common max power you're producing when using the van? I'm guessing 100-120? If you scale that up by two you're already close to the 15A limit and you're nowhere near the max 4 panels would be capable of.

On the other hand, your batteries would recharge faster in the morning before the sun is even high up so MPPT would throttle down earlier anyway. Still, this is way to close to design limits for my taste. Are you sure you don't want to just get a 100/30 and not waste energy or worry about excess?

I was out this weekend and after a couple of coffees from the Nespresso machine and a hour of TV after sunset, my battery had dropped below 90%. By the time I had showered and got ready to go out the next day, the battery was back to full. The MPPT throttled back the PV and everything was fine. There was no heat build up in the MPPT either. This battery recovery at 2x speed will be very welcome late in the year and on days with less sunshine. I don't think the extra cost of oversizing was too bad and so far, I can't see a downside.

Will you really need to?

Also in a motorhome with 800W solar and a 50A 75/50 MPPT controller.

In mid summer I occasionally see a current limited 50A (c715W) into our 4 cell 300Ah LiFePO4 for an hour or so in perfect weather.

I have not measured the heatsink temperature accurately but it could never be described as hot. Very warm would be a more technical term. (-;

NZ