I've been trying to think how a similar sized person would do in my 25 footer.
Providing that he could make it up the steps - mine also rated for 300 lbs:
He wouldn't be able to use the toilet as it is squeezed in between the vanity and the wall.
He would not be able to use the shower.
He could not fit on my jackknife sofa, nor could he fit in my dinette.
Provided the bed could support him, that's the only place he could occupy in the entire camper.
His weight is an issue for camping in a small TT. My hope for this person as he struggles with grief over his loss is that he gets a new lease on life and decides to move on to a more healthy lifestyle in order for him to enjoy the things he wants to do in life. If he were my friend, I would have a conversation with him.
good luck to all involved.