While marketed as a muscle relaxant, cyclobenzaprine is essentially a tricyclic antidepressant (it's structure is very similar to amitryptaline). It is pretty strongly sedating, due to it's H1 antagonist properties. Subjectively, it feels similar to other anti-histamine sedatives.
It will most definitely intensify the sedative properties of the morphine. Whether or not this will improve the high you get from morphine is completely subjective. Some people think anti-histamines make opiates feel better, and some people think it actually makes it less enjoyable. I probably would agree with the latter personally, there is something inherently uncomfortable about them to me.
If you decide to try this, perhaps use a slightly lower than usual dose of morphine. 10-20mg cyclobenzaprine should be pretty sedating for most people. Taking more will doesn't really make it any better, it is definitely a "less is more" kind of drug.
good luck.