Take my advice and go with 1 18s..
It's much more ideal in that cabin....
Also use birch ply with bracing, mdf is to **** flexible, and it's stupid heavy...birch is nearly 2x as stiff..
if you do your original measurements with 85in^2 of port area you will be good..
No need to tune under 34..
single baffle but braced..
Sub on drivers side close to the side an bottom as possible..
Port 21.5"Hx4"Wx15.5"D..and put a 4"Wx20.25"D peace dead center of the port to act like a divider/brace..
for the L side you need a 4"wide peace by 21.5 high..
Don't need to brace it reall 5 screws will reinforce it enough..
To brace the box find the distance from the center of the sub to the beginning of the port opening Divide by 2 and put 2 pieces of 3/4 back to back cut at 45 degree angles(so it makes a point) screw and glue the together and put no more the 2 screws per side..
I recommended you cut the braces a hair long to where you have the mildly tap them in place, this ensures no flexing and a secure bond betweent the panels and braces..
It will knock your head off b..