I haven't tried Tails on my Qubes but the default "-DVM" is close to TAILS but the DVM does apparently keep some information...
Interesting, but I tried TENS once (Open source OS similar to TAILS developed by the US Air Force Research Labratory):
www.spi.dod.mil/index.htm
There tech support was not very good:) and since it is a .mil domain the https certificates are not trusted on their website...
I haven't used it in a while but I have copied my old notes below, in case it helps:
Create TENS:
Create App VM(No network access) → Download TENs OS → Verify signatures
Create Template-HVM
In Advance → Increase memory to +2000
check add additional drives
Choose HVMiso template for Backend domain → Pick TENS.iso file in Path