Even if the Luftwaffe had trashed the RAF, Operation Seeloewe was a still-born, dead-ended, not-ever-going-to-happen, non-event. The Germans simply lacked the amphibious lift-capacity in 1940, and with their sclerotic industrial base it would have taken years to overcome that deficiency. The Axis strategic capability of 1940 is almost invisible against the Allied capability of 1944 . . . and the latter was a near-run thing, and could have ended in disaster had the Germans been more strategically competent.
Assuming a best-case scenario for the Germans in 1940 - no RAF, no Royal Navy in the Channel, an unopposed landing - it would have been a matter of weeks before the bulk of the invaders were the "guests" of King George. The attrition rate of the supply barges during crossings would have left the invaders starved of every imaginable type of supply. The Channel gets choppy after the summer, and laden river barges are not particularly seaworthy.
More realistically: The Germans would not have captured any viable, undynamited, functioning ports within their limited reach. Once the Germans had landed, Bomber Command and the RN would have paid the struggling landing zones a devastating visit . . . night after night. Even daylight supplies making it to landing zones under Luftwaffe cover would have been inadequate, and would barely have made it off the few useful beaches and jetties.