I believe FortranForm will only use ‘e’ for exponents outside the range from -5 to 5, however NumberForm is very customizable and could be used instead, for example:
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An approach using constructs like NumberForm is certainly a good way to go. In this context it is worth noting that FortranForm is a funciton that was introduced in Version 1 of Mathematica and has not been updated since. So, though it is useful in some contexts, to be more “modern” one has to often write custom code for things like this using the much more versatile functions such as NumberForm and so on.