In the end though you just can not fly below your msa without being absolutely sure of where you are and you can't be sure unless you have multiple sources of information. If ATC have radar that is one possible source, so is a DME, VOR, NDB, IRS etc.
I have flown too many Radar controlled airports around the world where I still don't descend below the MSA until I am sure of where I am, and not simply by the controllers advice. It is the only way to stay alive in this job.
Sound advice. The Radar Terrain Clearance charts that RAAF AIS provide should be available to all. I've been on one flight when we were vectored below the alt displayed on chart. After questioning the controller we were promptly cleared to the correct alt.