Step 5: Last word
Although circumstances differ, on reflection it is very liberating and the idea certainly does work, not cost-effective but that's wasn't the point to moot. Certainly useful for a out and about camper.
How can it be improved?
Interestingly Texas Instrument has a boost converter, TPS61200, that works down to 0.3V providing a regulated output up to 5V. This particular chip is well-sited solar powered applications, anyone interested may well explore further.
I would assume since a solar panel is augmenting the battery, its dimension could be halved (e.g. using a lithium polymer battery commonly used by RC hobbyist), doubling up real estate for additional circuitry.