Hi Rwashaph, from which county is this area? Besides am happy you mentioned that nobody is growing watermelon those regions i guess this creates suitable market niche for you before considering other regions you only need to do it right agronomically and with proper timing when local demand/ consumption is at its peak because it's fairly profitable to service local market than targeting cross-region markets which will automatically demand other extra costs.Before you venture into this have ever considered finding out why farmers around your place haven't been doing it? could it be natural factors that will also impact negatively on your case? with natural factors I refer to soil conditions, temperatures and certain wildlife as pests? Please establish suitability of that area in regard to these elements before investment.
NB. Market isn't a problem already you've more than what you service around you, once started doing it then let people know that you're growing them. I believe you're a.member to at least one FB group, WhatsApp, etc.what do you think sharing updates from your farm to them regularly and guess how you will meet an overwhelming interests and demands.
Blessings