Our reasoning & expectations behind this.
It was always our intention to install fairly large leisure batteries (and eventually a lithium system).
However, space is always at a premium so mounting them in an underslung box seemed a good idea despite the extra work needed; it also helps to keep the weight as low as possible, and putting the starter battery there as well frees a of space in the van (we plan to use for the fridge/freezer compressor). We also intend to fit a second box but this will require a bit more work than the first, as the pipework & handbrake will need rerouting, plus a cable gear linkage will need to be fabricated and fitted, and probably a few other bits as well, but we will get there.
The first hole in the floor.
Frame for the second box under construction.
More info and Photos and a full write-up to follow soon.
In-use reviews for this
Our conclusions.
Pros.
Larger batteries can be used.
Battery weight is lower so lower center of gravity.
A reasonable amount of extra storage, (even moor with a lithium system).
Storage is suitable for heaver seldom-used items.
Additional storage or usable space where batteries were.
The storage is accessible from within the van.
Storage is not obvious.
Shorter route for the power cable to the engine, (starter motor).
A small amount of weight distribution is possible.
Cons.
Quite a lot of work to install, (especially the second box).
Whirring and pipework need rerouting, (for the second box).
The right-hand box requires a different hand brake linkage system.
The Full-size right-hand box requires a different gear linkage system.
Batters and boxes are vulnerable to possible damage.
Loss of some ground clearance.
Some additional weight.
Other related or affected
Flooring.
Gear linkage system.
Hand brake
Pipework.
Wiring.
Plywood floor with hatch to access storage /battery box.