As been already suggested, I also add water and a "packet" of the chemical stuff while it is away in storage. Typically I dump at the campground and after unloading everything else at home, I'll go back in and pour about 4 gallons of water down the toilet, about half way through I toss in a packet. Always leave a little bit of water on the top of the flap as well, seems to keep the seal in good condition.
On our 1st trip ever, we added the packet, used the toilet, dumped and took it to storage. Everything seemed fine until the second trip when we first opened the flap to the toilet. Yes there was a smell lol. It didn't stay around for very long, but it was present for at least the first part of the first day. I asked around, and thats when others told me they always add a bit more water back in and another packet.
We have done this method since and have not had any issues since. I know some use a different method, and whatever works, well..works I guess. :)
I've also forgot to put water back in and taken it to storage. I usually go back within a day or two and bring 4 gallons and a packet with me, and just add it in right there without the "sloshing" effect of driving it with some water in there. Never had a problem with that either.