I'd go ahead and do it now when your being gone is more a vague notion than "but you're going to miss my dance recital/baseball game/etc." I have a two-year-old, and DH travels pretty regularly. DS asks where Daddy is, but usually is comforted by my straight answer ("a work trip") and an offer to send Daddy a picture. We send lots of pictures. Video chatting helps too if schedules work out (west coast travel not so much, but otherwise).
You ask about how this will impact your child, but you should think more about how it will impact your marriage. Will the travel be predictable or last-minute? Will you get a per diem or have to file receipts for reimbursement? Will you get any down time/comp time after trips or is the travel just straight up extra hours? There's a lot your DH will have to do when you're not there, so household logistics need to be worked out.
It's a given that I do all drop-off, pick-up, cooking, chores, kid illness care, etc when DH is gone. It helps me that DH's per diem is generous, so every trip he takes covers DS and I getting takeout once and/or a nice date night when DH gets back. DH can often take a down day after a lot of travel, and he uses that time to get projects done around the house that don't get done when he's gone. When a trip is long, I schedule some time to go do something for myself once he's back, and DH gets one on one time with DS.
The main challenge is not care for DS or how DS handles it, but how to handle household routines that get thrown for a loop when you're gone.