Instant Gas Hot Water system

Looking at putting an instant LPG gas hw system in a caravan for hw to the sink and for the occassional shower. Caravan is typically parked on a bush block with no 240v (although the van does have a substantial solar/bty setup). Prefer a system that is fully automatic & no external power requirements as different people use the van & I want to keep it as simple as possible. 2 systems i have found are:
1. 6 l/min unit from www.ausj.com.au which uses D cells to automatically light the gas. approx $350
2. Bosch 10H (same as Bosch WR 250-1 ?) unit which is 10 l/min & uses 'hydropower' (no elec required) to light the gas. approx $650

Anyone used either unit or know of similar systems that might meet my needs?