Would not the expansion and contraction ba at a minimum? The concrete and rubber really wouldn’t be exposed as it would be under water. My pond is constantly being filled from ground water from a sump to stop my bunker from flooding. That keeps the water temp fairly constant
I want a skimmer to help stop the leaves collecting in the pond.
Uv affects rubber more then temp does as far as longevity temps within day to day reason
Where you are placing the skimmer are you creating a Stream channel with the new concrete pad you poured and are going to have the barrel strat at the end of the our and build side walls or is you skimmer sitting on that new concrete? and if it is sitting on it why opening the pond down to the bottom of the skimmer ?
Without knowing what your plan is in the skimmer foam blocks, pad, filter basket, pump it's hard seeing what you planning or how to seal it up i know i would not build a skimmer area again i would do a negative edge or overflow . skimmers are becoming old school.
There are ways to make a "seal" from concrete to rubber; i would go over board and cut a slot and insert the rubber in a bed of pls30 both in the cut Before the cut and over the cut when rubber is inserted. You can apply a primer on the concrete to help hold the rubber to the concrete but it will do very little over time to keep it water proof. I would have bitchathane under the rubber back from the where the rubber was placed in the cut and SECURE WITH A TERMINATION STRIP.. HOW TO SECURE TO YOUR dyi skimmer has it's own issues but that is not your question