In many hybrid cars NiMH batteries are used. Advantages are better power to
weight
ratio and (I believe) up to 500 deep (near 100%) discharge cycles.

I'm wondering if NiMH would be a good alternative for frequent campers.
Purchase price is much higher than a conventional wet cell battery, but
comparable to the high end gel and AGM ones.

Cheapest I found is about $6/cell for 10Ah individual (1.2V cells).
(e.g. http://www.batteryspace.com )
Hence building a 10Ah 12V pack is $60, 20Ah $120, 40Ah $240 etc.
Because they are tolerant to deep discharges, one can buy less capacity
than for a lead-acid.

For example running an LPG furnace for one night one might need about 20Ah.
(The German Truma uses ~20W at full power and less than 10W at half.
20W @ 12 V is 1.7A, and for 10h use is then 17Ah.

A remaining problem is that most inexpensive chargers one can buy
are for slow charging (ie 10+ hours). For typical travel and camping use
I would prefer a charegr that could fully/mostly charge the battery in
a couple of hours of driving between campsites.

Martin