ASSIGNMENT 2 mouse - trying to make solid

knitting

I found the reason it wasn't splitting properly was because it wasn't made into a proper solid body. but when I do the fill surface on the bottom of the middle split housing, i tick the boxes 'merge' and 'make solid' and it doesn't turn solid no matter how many times i do it or try to alter the shape of my mouse. I've been trying to knit all the surfaces together  and ticking tyhe make solid boxes or using the thicken tool, but it won't do the whole lot due to surface colllisions (I'm guessing, as it just states it can't do it).

.....at this point ARRRRRRRRRRRRRRRRRRRHGGGGGGqekrdsewm