Odour be gone are sodium percarbonate - same as the nappy powders in my article on the link. Note the advice if changing from a nasty chemical to thoroughly cleanse the cassette.

If emptying every day you don't need to add anything.

Rather than set up a portaloo just for overnight - you can always use a 'night bucket'.

What about installing a SOG system, it's an extraction ventilation fan that just sucks any nasty's out side, just google SOG for your nearest agent.
We have one, no chemichals required, works well.

While we prefer to use ours only for #1's, sometimes there really isn't a choice. We haven't really found smell an issue. We don't use those purchased chemicals, which I think smell awful just by themselves. We use Napisan (actually Coles home brand nappy soaker) which works better, smells better and is so much cheaper. Just add a heaped capful to the bottom tank with a little bit of water.