Where to seal

I'm changing the plan as I go - so much so that I'd forgive anyone who alleges some initial lack of planning.
A biggy is the change from single skin roof to internally lined.
I was just going to connect the two side walls with 30mm by 19mm spars and fit a single skin, leaving them exposed inside. The walls buckled a bit so I decided to make the top flat section a double skinned box. The strength from such a light structure is amazing, it holds the walls nice and straight.
Then I fitted the front lower panel.
Then I decided it really needs an inner 'headboard" panel so I am not pushing against the outer skin with the pillows if I sit up in bed.
At that point I realised I only needed one more 5 x 3 sheet of ply to have a complete double skin. So I am shooting for that, using a piece of feather light appearance grade 3mm interior ply.
That's all great, but do I need to seal the inside of the outer skin? I didn't do it before I put it on as I wanted to glue to raw wood.
It'll be a messy job, and it''ll be hidden by the inner skin, but if I'll be risking the camper down the track by not doing it, i'll persevere.
Opinions?
A biggy is the change from single skin roof to internally lined.
I was just going to connect the two side walls with 30mm by 19mm spars and fit a single skin, leaving them exposed inside. The walls buckled a bit so I decided to make the top flat section a double skinned box. The strength from such a light structure is amazing, it holds the walls nice and straight.
Then I fitted the front lower panel.
Then I decided it really needs an inner 'headboard" panel so I am not pushing against the outer skin with the pillows if I sit up in bed.
At that point I realised I only needed one more 5 x 3 sheet of ply to have a complete double skin. So I am shooting for that, using a piece of feather light appearance grade 3mm interior ply.
That's all great, but do I need to seal the inside of the outer skin? I didn't do it before I put it on as I wanted to glue to raw wood.
It'll be a messy job, and it''ll be hidden by the inner skin, but if I'll be risking the camper down the track by not doing it, i'll persevere.
Opinions?