Skip it. Turns out to be a bad idea.
Running several Puppys it makes more sense for me to use ONE portable (accessed by all) than install the same application (or a version thereof) into each Puppy. I already had smtube-20.1 set up as a portable which I could use with Bionicpup64 and Fossapup64. Hence my reference to it. But the version doesn't make any difference. Downloaded smtube-20.6 and it works as well from those Puppys. But to get either version of smtube to work required installation into those Puppys of libraries, primarily QT5s.
There are two ways to handle that: (1) the libraries can either be installed into each Puppy or (2) as fredx181 showed with Portable firefox, an 'extralib' folder can be created within the application's folder and the application started with a script containing instructions such as this:
LAUNCHDIR="$(dirname "$(readlink -f "$0")")"
LD_LIBRARY_PATH=$LAUNCHDIR/:$LAUNCHDIR/extralibs${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH} "$LAUNCHDIR/smtube" "$@"
The last 2 lines displayed are actually one line in the script.
I had hoped that structure would avoid 2 problems. One has been around for long time. Slackware (and consequently Slacko under which and for which you created smtube) and debian/ubuntu locate 64-bit libraries in different folders. AFAICT, it does solve it.
The other is that while often libraries compiled under one OS will function under a different OS sometimes they won't.
Under Bionicpup and Fossapup 'ubuntu' libraries satisfied smtube's QT5 dependencies. Under VanillaDpup64 and Void64, they can't. I suspect that I ran into the same problem +Me ran into. Should have read the responses to his post more carefully. 
