Not that I know of. MHT is pretty good if you can get past not wanting
to have it read from a local file.

I understand that you don't want to have to manage those files, but you
might also want to consider that you are probably going to want some
caching mechanism for these anyways depending on your database.

Also, consider that if you use Navigate, you will be able to use the
built in Back/Forward to page through previously loaded pages.

It doesn't seem too terrible to have an application folder sub-directory
to write these files from the database. When the application fetches an
mht from the database, it can create the directory if needed and write
the file there. When the application exits, it can just remove the
directory.

Another approach might be to tackle this from the MIME perspective. You
can parse these files with a MIME parser so you may be able to figure
out how email clients render emails with html bodies.

Regardless, when I come across situations like these, I typically use an
approach that I know how to get working and move on. I create an
Interface for it where I can easily swap out the behavior with another
implementation if a better solution can be found.