The mains water line is under pressure all the time even when using your pump it will pressurize as far as the NRV, with any of them when you realize there's a leak its already too late not to mention the housing they live can leak at some point.............
You could always sacrifice a bit of draw space or just move the whole shebang elsewhere, in my 14.44 the battery was at the bottom of a wardrobe, no room for another battery and if you wanted to get at it, damn near impossible so I just moved the whole lot to under the dining seat, never had a big invertor back then but it might have squeezed in.
Pity they didn't put the water run over the wheel arch, they have to bring the pipes inboard so they clear the chassis rail I moved my water pump to under the floor which allowed me to cut back on numerous plumbing in a cupboard along with about 13 possible leak joints moved outside, when I changed my mains inlet I just ran it under the chassis rail to side of van where I fitted a bracket for it, a much firmer fitting all round.....
The invertor intstalation instructions should give their ideal cable run length, further you go the larger the cable size, I think mine said 700mm actually for the cable that came with it but not a drama as mine sits next to the batteries the thing is you might be better off putting it outside the battery space, that will enable you to actually get at it to switch on/off easily and quickly, you don't want to leave them on all the time as they will drain your battery, main has a wired remote which allows me to have it in the power station in boot and turn it on from inside van......... mine is just for charging laptop, drill batteries etc ......