Rehearsal dinner insert?

Here are some examples http://www.pinterest.com/thedilettante/invitations-rehearsal-dinner/

I'm sending out a separate invitation a month before the rehearsal since my wedding invitations will go out 6-8 weeks before.

We sent out a separate invitation for the RD, you can always do a post card.

I'd like to give people as much notice as possible since most of our wedding party is out of town and the rehearsal is on a Thursday. Is it strange to include with the invite?

It is a very casual dinner that we hosting ourselves.

Ones I've been to in the past were e-vites. I thought that was pretty easy. I'm thinking I'll do something like that, unless my future mother-in-law would rather send out paper ones.

My rehearsal is also on a Thursday and have several people from out of town who already plan on being there. The invitation is just a formality so you can always text/email out of town family and let them know the date and time and follow up with an invite or evite later.

I have never heard of doing a insert with the wedding invite. I am just doing simple separate ones for the rehearsal dinner. My OOT guests already know about it and plan on coming. I would be afraid of a mix up with doing a insert with the invite and putting some in the wrong invite and that would also add weight to the invites.