I bought a couple of tubes recently to stick down a flexible flood barrier across my driveway! It's billed as an adhesive/sealant and I used it for both purposes.If it lives up to the description then it is good value but is a bit messy to use. White spirit seems to shift it when it is still wet though.
I am usually reluctant to stick things like motor mountings down as you have a problem if you need to subsequently alter their alignment for any reason. When I built one of the SLEC Faireys I found I needed a different coupling which required the motor to be shifted back a bit. Fortunalely it was just screwed down onto a base.
Colin