partially-remembered SF books (aliens, camping, and a moose)

There are a couple of books I read in the 1970s, that probably dated from a decade or more earlier, that I've never been able to identify or find again.

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  The first was a book (and its sequel) about a young alien named something like Martin, Marty, or similar, who comes to Earth, and goes camping (and/or joins the Boy Scouts) with the protagonist young Earthling boy. The sequel was about Martin/Marty/whomever returning the favor by inviting the boy back to his home planet, where they go to a perfectly-reconstructed campsite that is otherwise located in the middle of an empty wasteland. I seem to recall that there were a lot of illustrations.

  
  


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  The next one I remember very little about, except I think it involved a boy and girl who somehow make the acquaintance of an alien that resembles an anthropomorphic moose (yes, really). There was some plot element about how the moose-thing could teleport them, but there was also some sort of shrinking force-field around them that they couldn't leave, possibly generated by the moose's antlers. The reading level for this one would have approximated that of the Mad Scientist novels, and the few illustrations were similar in style to those in the Mad Scientist books as well.

  
  

Any help would be appreciated!