tell us more.
do you have any louvres or vents in the bonnet at all.
is the firewall sealed from the cockpit. youll be surprised how many aren't. check all the sides and top , grommets fitted etc
what engine is it..do you have a heater . is it stuck on hot.
we can give some good advise from there.
but simply exhaust wrap makes a huge difference.although not all will say its a benfit. ive run it for 4 years with no issue. and it isn't expensive