Here's my answer:

From this point on, there is no spoiler text, because it makes it easier to format, at least for me.
T E N I N E
F I O N E V
O G X R V I
U H H I E F
R T W O S Z
I started by figuring out the letter density in the overall puzzle. The letters break down as follows:
E 10
N 5
I 4
O 4
T 4
R 3
F 2
H 2
S 2
V 2
G 1
U 1
W 1
X 1
Z 1
Next I started working on the 3
squares. Since all three are in a diagonal, I started with the assumption that they are within the same word. This requires a word of length 5
, which means it is one of: SEVEN, EIGHT, THREE
Only one of those includes three of the letters that occur at least three times from above, so that line became THREE
Since H
only occurs twice, I ran the THREE
diagonally up and from the left.
.....E
....E.
...R..
..H...
.T....
First thought would be to place the EIGHT
, as that shares the only other H
, but that doesn't fit. H
is on a single letter space, so let's leave that for now.
Looking at the 2
and 2 3
s in the upper right corner, it seems like there should be quite a bit of overlapping there. Let's try placing the NINE
and TEN
as follows:
..NINE
....E.
...RT.
..H...
.T....
Not bad, could be promising.
So far, we have the following for letter counts
..1122
....2.
...11.
..1...
.1....
Uh-oh! We only have one end N
left and it's on SEVEN
. That won't fit in our open space. Let's try putting SEVEN
where TEN
is.
..NINE
....E.
...RV.
..H.E.
.T..S.
..1122
....2.
...11.
..1.1.
.1..1.
How about we run the EIGHT
in the second column?
.ENINE
.I..E.
.G.RV.
.HH.E.
.T..S.
.11122
.1..2.
.1.11.
.11.1.
.2..1.
Ooh, I see almost all of TEN
. Let's finish that.
TENINE
.I..E.
.G.RV.
.HH.E.
.T..S.
122122
.1..2.
.1.11.
.11.1.
.2..1.
Now, we can add TWO
off the T
from THREE
and ONE
off the first E
TENINE
.IONE.
.G.RV.
.HH.E.
.TWOS.
122122
.1113.
.1.11.
.11.1.
.3111.
Hey, let's finish off ZERO
TENINE
.IONE.
.G.RV.
.HH.E.
.TWOSZ
122122
.1213.
.1.21.
.11.2.
.31111
And we can run FIVE
up the right side and FOUR
down the left. Note, FOUR
could be either up or down, whatever floats your boat.
TENINE
FIONEV
OG.RVI
UHH.EF
RTWOSZ
122123
112131
11.211
111.21
131111
And finish off with SIX
TENINE
FIONEV
OGXRVI
UHHIEF
RTWOSZ
122123
112131
111211
111121
131112