Clyde,

What about venting it into the crawlspace below?

You don't want to vent a dryer ANYWHERE inside the house, including the
attic or the crawlspace. That's a lot of moisture that could cause rot,
mold, etc. I also believe it's a code violation.

I ask because to get the vent down and out through an outside wall
will require about 3 90 degree bends along with about 40+ feet of
ducting.

Unless your house is 80'x80' and the dryer sits right in the middle, I'm
guessing you can find a shorter route to an outside wall. I believe the
maximum length is supposed to be under 25 feet, which you have to subtract
5 feet for every 90 degree elbow (just going from memory on this).

I had a similar situation when I built my house. My initial options were 16
feet up to the roof, or about 20' out to a back wall. Once I stopped
overthinking the situation, I ended up with a short 5' duct run to a side
wall. I went down to the crawlspace, under the joists, then out through the
rim joist in the crawlspace. Two 90's, two 45's, and about 4' of actual
duct. I wrapped the whole thing with metal foil tape and insulation. It
flows wonderfully and can be cleaned easily from outside.

Check your options further. You'll probably find another route that is much
shorter...

Anthony