You must practice situps on your alone time but you can always ask someone to hold your feet or you can wrap your feet against something so you wont move..a great advice for sit ups is to breath in when coming down and breath out when going up!!!
For those waiting to get letters it really depends when they can write for me it was immediately but sometimes your soldier is training in the outdoors and wont return for a couple days. Usually your soldier gets to write during personal time only!!!
How freaking cute is this omg hopefully I am here for halloween I have an idea for a custom ; p