Cast iron is a lot more durable than most of the busybodies on the internet would have you believe (yes, I do realize I'm a person on the internet, but I'll say my piece anyway.) I used to avoid tomatoes and take great care trying to avoid any trauma cleaning the pan, but after years of use I realized none of that is necessary, use the pan and it will mostly take care of itself.

These days I wipe the pan out after I use it, and hit it with some hot water and dish soap. Scrape off any gunk that's stuck on there and dry the pan. Drying them after you clean them seems to be the most important step, other than that they don't need much care. The next time I use the pan I put it on the heat with a drizzle of whatever oil is handy and it's ready to go.
I think most of the problems people blame on cast iron seasoning are more related to cooking technique instead.

If I'm not going to be using it for a while I wipe it down with some kind of cooking oil for storage, but other than that they don't need any special treatment.

I agree with Perception about how cast iron, properly seasoned, can take a lot of abuse. The whole dish soap thing. Unless you're using soap from before the 1960s, it's unlikely to have lye as an ingredient, so it's almost impossible to strip proper seasoning off cast iron. Tomatoes are rather mildly acidic, unless you are making Italian Sunday gravy every day, it's unlikely to cook long enough to do any damage at all.