Filling out forms for travel agency - need advice

I need some advice! I am filling out forms for the first time for a travel agency. Everything looks very professional, no red flags, etc. I just have one problem. Its this:

Since being an RN I've worked on the same floor for a total of 19 months. My husband has been out of work since February and just got a job out of state. He is actually traveling to his new job today. I am ONLY leaving my current job due to my husband having to go elsewhere for work. I don't know how long it will be until the "right" travel nursing job opens up... but one of the forms wants my current employer to fill out an evaluation form about me. I am not worried about getting a good recommendation. What I'm worried about, is that I was not planning on telling my current employer until 2 weeks to a month before going elsewhere. The travel agency does not have openings where my husband is now, but said that they would within a couple of months.

What do you all do about having a current employer fill out an evaluation form while you are still working for them? Should I just tell them and hope they are ok with me leaving? I don't want to NOT have something lined up yet, and my current employer try to replace me before I'm gone, kwim? (My employer knows my husband is out of work and has hinted that they don't want to lose me.) What should I do?