Hi Francis,
A few additions which have really helped:
1. we had an LPG conversion, which paid for itself over 24000km (approx 14500m), Lpg is cheaper, both here and abroad, and somewhat better for the environment than petrol. The LPG filler is tee'd to fill the Gaslow for cooking as well as fuel tank.
2. Also, we had a canopy-type awning fitted, originally thinking it would be useful shade, but actually it really comes into its own in the UK climate when extended about a third to act as a rain porch/drying area (avoids it flapping about in foul weather when fully extended).
3. We had blown air heating fitted, but hardly use it - a small oil-filled radiator is much quieter on chilly evenings. Worth noting, however, neither heater would be good for wild camping because of the electricity draw...
Glad you've opted for underseal - a must!