Join Cab to Body ?

Hi all,

My first post here.

I'm thinking of buying a Toyota Dyna or other small truck to use as a small simple campervan.

I've had a look at a few and like the size in the Cab and there's a lot of used Pantech options for mounting on the body.

BUT... I'd like to be able to get from the Cab to the Body without getting out of the vehicle, for security in case I stop by the side of the road somewhere at 2am for a nap while travelling.

As I've never owned a truck before i'm not sure if this is legal ?

I was guessing I'd just cut a hole big enough to crawl through, and join it with a rubber accordion boot of some kind. This is just my crazy head thinking, I have not actually seen anything like this myself. Any practical advice and suggestions are very welcome.

Thanks.